"So I go to meet [Zack Snyder] and he's sitting there and he's telling me, 'You can't read the script, so I'm just gonna tell you what happens'. And he spent like a half hour telling me every scene in this movie," Shannon said at the River Run International Film Festival.

"He's at his home in Pasadena and I'm looking out at the Rosebowl, there's little humming birds flying around. [It's like] I'm on acid! Then it's a month later, it's like 'Okay, you're General Zod'."

The Boardwalk Empire actor added that he was then asked to do a filmed audition with new Superman Henry Cavill so that Warner Bros could see if they had "chemistry".

Asked if he has seen any of the previous Superman movies, Shannon replied: "I've seen the one with Terence Stamp as Zod... Christopher Reeve, that was a great performance, that's a hard part."